Mechanical thrombectomy devices such as clot retrieval devices or stentrievers are frequently used to recanalize blocked cerebral arteries in patients suffering from acute ischemic stroke. The method of use of such a device typically involves positioning a large diameter catheter in a location proximal of the obstructive clot, and then advancing a microcatheter and guidewire together to a location distal of the clot. The guidewire is then withdrawn proximally to allow for the introduction of the clot retrieval device in the collapsed configuration through the microcatheter. A generic clot retrieval device is comprised of an elongate member and a clot engaging body connected to the distal end of the elongate member. The clot retrieval device is advanced distally within the microcatheter until is it situated within the clot. At this stage the microcatheter is withdrawn and the device will expand. As the device expands it engages and captures the clot. Once the clot has been captured by the engaging body of the device, aspiration is typically carried out through the large diameter catheter while the device and the clot are withdrawn towards the large diameter catheter (which may be a guide catheter or a sheath or a distal access catheter). The device and the clot are withdrawn into the large diameter catheter and removed from the vasculature.
The force required to retract the device may have undesired consequences. In order to dislodge the clot from the vessel a force must be applied to it through the stentriever device. This force is effectively applied to the vessel in which the clot is lodged and to the distal vascular bed, placing these vessels in tension and placing the vessels proximal of the clot in compression. Once the clot begins to move there is relative movement between the stentriever device and shaft and the vessel wall. This relative movement can cause abrasion and damage to the endothelia and underlying layers of the vessel wall, which may result in a dissection or perforation, or could give rise to the subsequent formation of thrombus which could then be liberated to create an additional stroke.
The force that must be applied to dislodge and retract the clot is dependent not only on how well lodged the clot is in the vessel, but also on the frictional losses that occur where the stentriever device contacts vessel walls or the inner surface of the catheter through which it passes. Thus it would be advantageous to have the use of a device which acts as a shield between the elongate shaft and the vessel wall. In the preferred embodiment the invention would remain in situ in the vessel as the elongate shaft is being retracted and absorb the tension which would normally be exerted on the shaft and the vessels. Preferably the invention would have a low friction inner surface and a higher friction outer surface. This would allow the shaft to move more fluidly within the device while the device remained in the vessel. The present invention includes these features and improves upon the methods of clot retrieval previously discussed.